Injection refers to:

• A. The external pump method to force foam concentrate into the fire stream at the correct ratio for the flow desired.
• B. The device that injects foam concentrate into water stream to make foam solution.
• C. The finished foam after air introduction.
• D. The foam expansion process.

Answer: (A)

Injection is a foam proportioning method that uses an external pump to force foam concentrate into the water stream at the desired ratio. This setup relies on a calibrated metering pump (and associated valves) to deliver the concentrate into the water so the final foam solution is produced at the correct concentrate-to-water mix, regardless of changes in water flow. This is different from the other choices because it describes the active introduction of concentrate into the stream by pumping, not just a component that injects into water, not the finished foam after air is added, and not the foam expansion process.